Fluid applicator apparatus



APril 6 1965 R. c. HANSEN 3,176,653

FLUID APPLICATOR APPARATUS iff/l f5 V7 (fr M47 f3 April 6, 1965 R. c. HANSEN 3,176,653

FLUID APPLICATOR APPARATUS Filed Feb. 20, 1963 2 Sheets-Sheet 2 f ff 65 7) 2/ J 4f! 4 if /Zl fan/Pffffae IN ENTOR. Bzw/m0 bfi/ww Y United States Patent Ont-ice lFatented Apr. 6, 1965 3,176,653 FLUlD APPLICATR APPARATUS Richard C. Hansen, Collingswood, NJ., assigner to Radio Corporation or" America, a corporation of Delaware Filed Feb. 2l), 1963, Ser. No. 259,359

Tnis invention relates to apparatus for applying a iluid composition to a surface and more spcciically to improved apparatus for developing electrostatic images on an electrographic or insulating surface with a fluid cr liquid developer composition.

ln the art of electrostatic printing, electrostatic images are produced on the surface of an electrographic or insulating material. Visible images are commonly produced therefrom by applying to the surface {indy-divided developer particles. The developer particles deposit on the surface in substantial conliguration with the charge pattern to produce a visible image. Several methods of producing visible images are described in Electrolux Direct Electrophotographic Printing on Paper by C. l. Young and H. G. Greig, RCA Review, -ecernber 1954, vol. XV, No. 4.

ln the art oi electrostatic printing a liquid developing process has been proposed in which solid developer particles are dispersed in an insulating carrier liquid. Liquid development provides many advantages over the use of dry developer mixtures and over other methods for some applications. Liquid development can be accomplished by flowing the developer composition over the surface to be developed or by immersing that surface in a tray of liquid developer. The developer may also be sprayed or rolled onto the surface. Liquid development and suitable cornpositlons therefor are described in U.S. Patent No. 3,053,688 issued September l1, 1962 and US. Patent No. 3,076,722 issued February 5, 1963, both to Harold G. Greig.

Ot the techniques, mentioned above, for applying liquid developer compositions to surfaces, the use of a roller to carry the liquid developer over the elctrostatic imagebearing surface is the most satisfactory when high developing speeds and high contrast are desired. Roller techniques require that considerable care be exercised to prevent smearing of the image and that steps be taken to prevent oiiset printing of ghost images carried on the roller as it rolls over the surface being developed. Any techniques employed in developing electrostatic images are further complicated when the result to be achieved is a reverse image. The term reverse image is used hereinto describe the image produced when developer particles are attracted to and adhere in areas on an insulating surface bearing no charge or reduced charge by electrostatic repulsion from charge-bearing areas. The production ot high quality images, with minimum deposition of developer particles in non-image areas, is more diilcult with a reversal development technique than with a direct developrnent technique.

Accordingly it is a general object Of this invention to provide improved apparatus for image development with iluid or liquid developer compositions.

Another object is to provide improved liquid developing apparatus including means tor improving image contrast.

Another obgect of this invention is to provide improved apparatus for developing electrostatic images with a liquid developer composition at high speeds.

Yet another object of this invention is to provide irnproved developer apparatus which includes control means for decreasing the deposition of developer particles in non-image areas on an electrostatic image-bearing surface.

A still further object of this invention is to provide improved developer apparatus having electrical control means for enhancing reversal development electrostatic images.

These and other objects and advantages are achieved by the improved apparatus of this invention which includes conduit means for bringing uid or liquid developer composition to an image-bearing surface. An opening in the conduit means provides for egress of the developer composition and contact thereof with the surface to be developed. Adjacent the opening, an electrode is provided to which electrical potential can he applied during develop ie f.. Both the electrode and the opening in the conduit means are spaced from but in close proximity to the surface being developed and provide means for enhancing reversal development and for insuring maximum control of development when appropriate poterltial is applied to the electrode.

@ther objects and advantages are included in the iollowing detailed description and in the drawings, wherein:

FUURE l is an end view in elevation and partially schematic of improved apparatus in accordance With this invention;

llGUl-E 2 is an end view, partly schematic and partly in section of an applicator head of FlGURE l;

@URE 3 a bottom view of applicator head of FEGURE l; and

FGURE 4 is a sectional end view, partly schematic, an alternative embodiment of the improved apparatus this invention.

Similar reference characters are applied to similar element throughout the drawings.

FiUURE l illustrates the general structure of an irnproved apparatus made in accordance with this invention. Te apparatus includes an applicator head l1 adapted to move lat- :ally over a sheet i3 of electrophotographic paper resting on a metal support 15 which is connected to a source of reference potential or to ground l. Movement of the applicator head M. is provided for by a reversiblc motor 19 coupled to a pulley 21 which in turn is coupled to the applicator head l by a bead chain 23. A compressor 2d supplies air to the applicator head 11 through flexible tubes 2S" to provide an air curtain between the base of the applicator head lil and the paper sheet i3 as will be described hereinafter. A source 27 of bias voltage is connected to a terminal 29 on the applicator head through positive and negative potentiometers 3G and 3l and a double-throw switch 33. With an applicator head ll made of metal, bias voltage can be applied thereto to establish it at a potential direrent in value from, and of either polarity with respect to, the potential on the Aeal support l5. While it is entirely feasible to apply bias potential to the applicator head 1l, it is preferred that one or more separate electrodes be provided for this purpose within the applicator head as is shown in FEGURES 2 to 4.

The construction of a suitable applicator head 11 is shown in greater detail in FIGURES 2 and 3. The applicator head l1 is `constructed from a metal block i2. A wide elongated slot 35 is provided to contain a supply of liquid developer which is poured into the slot 35 through a hole 37 in a cover plate 39 on the block 12. The bottom of the wide slot 35 is closed, except for a narrow slot 4l, by a metal plate 43 supported on an insulating block The narrow slot 4l provides for the egress of liquid developer so that it can corne in contact with the paper 13. An adjacent chanel 47 feedof of ing into a cut away section 49 in the insulating block 45 lprovides a return path for excess developer composition after it has contacted the paper sheet 13. Near the .y rectangular channel Sl, which is partly closed at its lower end by means of a baille plate 53 to provide a narrow rectangular slit 54 through which air can Ibe ejected to impinge upon the surface of the paper sheet 13. Air is supplied to the rectangular channel 51 through a series of holes 55 connecting 'with the flexible tubes 25 and the compressor 24. An additional U-shaped channel 57 provides means for air to escape through a series ot` holes 59 in the top of the applicator head.

In the device shown in FIGURES 2 and 3, the metal plate 43 is provided with a connection terminal 29 connected to the voltage supply 27 in the same manner as the terminal 29 in FIGURE 1 so that the metal plate 43 can function as a bias electrode. A rod, wire or series of parrallel -wires could Ibe substituted for the metal plate 43 to provide the function of a bias electrode.

To develop an electrostatic image on the paper sheet 13, air from the compressor 23,'FIGURE 1, is forced into the outer rectangular channel 51 at approximately 5 to 20 pounds per square inch. The air passes through the rectangular slit 54 and forcibly impinges upon the paper sheet 13. This causes the entire applicator head 11 to rise and maintain between its bottom surface and the paper sheet 13 a spacing of about .0005 inch.

Liquid developer is poured into the wide slot 35 and the applicator head is moved across the paper sheet, for example, from right to left as viewed in FIGURE 2. Liquid developer passes through the narrow slot 41, contacts the paper sheet Y13 and flows over the paper sheet 13 under the metal plate 43.

During the time the liquid developer is applied to the paper sheet 13, bias potential is applied to the metal plate 43. -By proper selection of the polarity and magnitude of bias voltage, several advantages can be achieved. Normally, with electrophotographic paper (paper sheet 13) such as that described in U.S. Patent No. 3,052,540 issued September 4, 1962 to H. G. Greig, the electrostatic image to be develpoed comprises a pattern of negative electrostatic charges. Such images can be developed with liquid developers consisting of a carrier liquid in which toner particles have been dispersed, such particles taking on a positive triboelectric charge in forms an air bearing or cushion to support the applicator the liquid. During development, the negative charge pat- Y tern on the paper sheet 13 electrostatically attracts toner particles from the liquid and causes them to deposit in the charged areas on the paper sheet. A tendency exists for Some of the toner particles ,to physically adhere in uncharged areas on the paper sheet 13 where they lare unwanted and reduce image contrast by producing a mottled or grayish background. With about 100 to 300 volts,

negative bias potential applied -to the metal plate 43, unwanted deposition of toner particles in background areas is substantially eliminated. The negative bias potential applied to the metal plate 43 can also be adjusted to prevent background toner deposit in those instances wherein background areas on the paper sheet 13 havebeen incompletely discharged, as by underexposure.

Developer compositions Iconsisting of special toner particles dispersed in insulating liquids are known to be capable of reversal development of negative electrostatic images. In such compositions, the toner particles, on being dispersed in the liquid, take on a negative triboelectric charge. When the dispersion is applied to a negative electrostatic image, the toner particles are repelled from the negatively-charged 'areas on the paper sheet 13 to deposit in the other areas thereon. been found that, when immersion development or a similar technique is employed, large image areas are difficult to till in with toner particles. With the developer apparatus described herein, this difficulty is overcome by the application of la bias potential such as, for example, to 150 volts, negative with respect to the support A15.

As mentioned heretofore, air passing through the rectangular slit 54 in the bottom of the applicator head However, it has head 11, but also produces an air curtain forming a barrier against'escape of liquid developer from under the aplicator head 11. Some of the air impinging upon the paper sheet 13 flows'outwardly and escapes around the periphery of the applicator head. A portion of the air also ows inwardly. That air which flows inwardly to reach the channel 47 picks up excess developer composition from the paper sheet 13 carrying it through the channel `47 and the 'cut away portion 49 of the insulating Y block 45 and returning it to the wide slot 35 in the applicator head 11. Inwardly ilowing air also escapes through .the U-shaped channel'57 and the series of holes 59 in the applicator head 11. In addition to the functions described above, the air which impinges on the paper sheet 13 also promotes drying of that sheet. When a highly volatile carrier liquid is employed in a liquid de-V veloper, the paper sheet 13 is substantially dry as soon as the applicator head 11 has passed thereover.

Added ilexbility in operation of the applicator head 11 can be and preferably is provided for by separating the function of supporting the lapplicator head 11 from the function of liquid developer confinement by the air which impinges on the paper sheet 13. As shown in FIGURE 3, this is accomplished by two additional slits 61 cut into the base of the applicator head 11 near each end thereof. VIsolation grooves 63 are also provided in the base of the applicator head y11 and yare located between the rectangular slit 54 and the additional slits 61.

With this construction, air may be supplied to the recdesigned to develop electrostatic images on a continuous web 13 of electrophotographic paper. The web 13 is carried over and supported by a conductive roller 64 to pass adjacent a curved applicator head 11'. Both the roller 71 and the curved applicator head 11 are fixed in position by means not shown to provide a spacing between the web 13' and the applicator head ll'of approximately .0005 inch. The applicator head 11 includes most of the features described in connection with FIGURES 1 to 3. A wide slot 35 is provided through which liquid developer is applied to the web 13. Instead of a single metal plate 43, as shown in FIGURES 2 and 3, this design embodies a pair of such plates 65 and 66 spaced adjacent each other to provide the slot `41 through which the liquid developer passed.

The pair of platesV 65 and 66 are, electrically coupled together and connected to the bias voltage supply 27 in the same manner as the single plate 43 of FIGURE 2. The conductive roller 64 is connected to a source of reference potential or to ground 17 as was the metal support 15 in FIGURE 1.

Liquid developer is supplied to the applicator head 11', 1n FIGURE 4, from a container or 4reservoir 69. A centrifugal pump 71 in the reservoir forces the liquid de- A As the roller 64 carries the web 13' in the direction of the I arrow 75, liquid developer is carried on the web 13 into the space between the web 13 and the upper metal plate 66. Some liquid developer can be expected to flow down` wardly over the surface of the web 13 particularly at slowweb speeds. Liquid developer owing downwardly passes into the space between the lower metal plate 65 and the web 13. When biasing voltage is applied to the pair of metal plates 64 and 65, two biasing fields are generated, one between the upper plate 66 and the roller 64 and the other between the lower plate 65 and the roller. The generation of these fields influences developing results in the same manner as the application of bias voltage to the metal plate 43 of FIGURES 2 and 3.

Excess liquid developer is removed from the Web 13', FIGURE 4, and returned to the reservoir 69. A rectangular channel 77, cut into the curved surface of the applicator head 11' and surrounding the wide slot 35', collects the excess liquid developer. Conduits '79 are coupled to the applicator head 11' and communicate with the rectangular channel 77 through holes 81 to provide means for returning the excess liquid developer to the reservoir 69.

As before, a rectangular air curtain is produced by means of a compressor 24 feeding through flexible tubing 25 and a rectangular slit 54 adjacent the web 13. Air flowing over the surface of the web 13 escapes into the rectangular channel 77 carrying excess liquid developer with it for return to the reservoir 69. In this embodiment (FIGURE 4), the applicator head 11' has been described as being fixed in position in relation to the roller 64. Thus, air impinging on the web 13 need not provide an air bearing for supporting the applicator head 11', although it may do so. If the air bearing is not provided, there is no need for the additional air slits 61 or the isolation slots 63 as described in connection with FIGURE 3. The embodiment of FIGURE 4 does function to provide an air barrier against escape of liquid developer as well as to remove excess developer and enhance drying of the web 13.

In the embodiments shown in the drawings, the applicator head 11 of FIGURES l to 3 has been shown and described as being positioned above the paper sheet 13. The applicator head 11 can readily be adapted to operate in a different position to develop electrostatic images on a paper sheet positioned on the under side of the metal support 15 or with the metal support inclined or vertical. Similarly, the applicator head 11 need not be in the position shown in FIGURE 4 but can, instead, be supported in any other position around the periphery of the roller 64. Also, the applicator head 11 could have a convex surface for developing electrostatic images on a concave surface.

What is claimed is:

1. Apparatus for developing electrostatic images on an insulating surface comprising:

a conductive member supporting said surface in a substantially horizontal plane;

an applicator head having a substantially planar base;

first conduit means formed in said head with an opening through said base for the egress of liquid developer composition;

second conduit means formed in said head with an opening through said base for the return flow of liquid developer composition;

means substantially surrounding said first and second conduit means for directing a current of air against said surface such that a portion of said air sweeps excess of said liquid developer toward said second conduit means to aid said return fiow;

a developing electrode having connection means for applying electrical potential thereto and establish a potential difference between said electrode and said conductive member;

insulating means on said head for mounting said electrode between said openings through said base portion; and

means for supporting said applicator head with said base portion and said electrode in close proximity to said insulating surface.

2. Apparatus for applying liquid developer to an electrographic surface comprising:

an applicator head including first conduit means having an elongated opening e. for bringing said liquid developer to said surface, second conduit means having an elongated openin." adjacent the elongated opening of said first conduit means, developer electrode means between said elongated openings, and third conduit means having an opening surrounding said elongated openings to provide a gas barrier against escape of liquid developer and remove excess developer from said surface through said second conduit means; and second electrode means arrayed with respect to said applicator head to receive said surface between said developer electrode means and said second electrode means.

3. Apparatus for applying liquid developer to an electrographic surface comprising:

an applicator head having an arcuate surface and including,

first conduit means having an elongated opening through said arcuate surface for bringing said liquid developer to said electrographic surface, second conduit means opening through said arcuate surface on either side of and parallel with said elongated opening for removing excess liquid developer from said electrographic surface, at least one elongated electrode between said elongated opening and the opening of said second conduit means, and third conduit means opening through said arcuate surface and surrounding the openings of said first and second conduit means to provide a gas barrier against escape of liquid developer; and another electrode arrayed in relation to said applicator head to receive said electrographic surface between said elongated electrode and said other electrode.

4. An applicator head for applying liquid developer to an electrographic sheet supported on a planar conductive surface, said applicator having a planar base and comprising:

first conduit means having an opening through said planar base for bringing said liquid developer to said sheet,

second conduit means having an opening through said planar base adjacent the opening of said first conduit means for the removal of excess liquid developer from said sheet,

developer electrode means between the openings of said first and second conduit means,

third conduit means having an opening through said planar base surrounding the openings of said first and second conduit means to provide an air barrier against escape of liquid developer from said sheet, and

fourth conduit means opening through said planar base outwardly from and on opposite sides of the opening of said third conduit means to provide an air bearing for supporting said applicator head above said sheet on said conductive surface.

5. Apparatus for developing electrostatic images on an insulating surface comprising:

a conductive member supporting said surface in a substantially horizontal plane;

an applicator head adjacent said conductive support;

first conduit means in said head having an opening for the egress of liquid developer composition;

second conduit means adjacent said first conduit means and having an opening for the return flow of said liquid developer composition;

a developing electrode, located between said openings,

having electrical connection means for applying ,theretol a bias potential with respect to said conduc-v excess air from between said head and said surface. 10

Refrncesoidf by tnqnxaniingrj UNITEp STATES' PATENTS Y Gundlach f 118,-.-,637 XT WILLIAM DMARTTN, Prima@ Examineh 

1. APPARATUS FOR DEVELOPING ELECTROSTATIC IMAGES ON AN INSULATING SURFACE COMPRISING: A CONDUCTIVE MEMBER SUPPORTING SAID SURFACE IN A SUBSTANTIALLY HORIZONTAL PLANE; AN APPLICATOR HEAD HAVING A SUBSTANTIALLY PLANAR BASE; FIRST CONDUIT MEANS FORMED IN SAID HEAD WITH AN OPENING THROUGH SAID BASE FOR THE EGRESS OF LIQUID DEVELOPER COMPOSITION; SECOND CONDUIT MEANS FORMED IN SAID HEAD WITH AN OPENING THROUGH SAID BASE FOR THE RETURN FLOW OF LIQUID DEVELOPER COMPOSITION; MEANS SUBSTANTIALLY SURROUNDING SAID FIRST AND SECOND CONDUIT MEANS FOR DIRECTING A CURRENT OF AIR AGAINST SAID SURFACE SUCH THAT A PORTION OF SAID AIR SWEEPS EXCESS OF SAID LIQUID DEVELOPER TOWARD SAID SECOND CONDUIT MEANS TO AID SAID RETURN FLOW; A DEVELOPING ELECTRODE HAVING CONNECTION MEANS FOR APPLYING ELECTRICAL POTENTIAL THERETO AND ESTABLISH A POTENTIAL DIFFERENCE BETWEEN SAID ELECTRODE AND SAID CONDUCTIVE MEMBER; INSULATING MEANS ON SAID FOR MOUNTING SAID ELECTRODE BETWEEN SAID OPENINGS THROUGH SAID BASE PORTION; AND MEANS FOR SUPPORTING SAID APPLICATOR HEAD WITH SAID BASE PORTION AND SAID ELECTRODE IN CLOSE PROXIMITY TO SAID INSULATING SURFACE. 